The entire disclosure of Japanese Patent Application No. 10-109915 filed on Apr. 20, 1998 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a navigation system which performs guidance along a route.
2. Description of the Prior Art
A vehicle navigation system performs setting a point such as a destination, a crossing point, a start point and etc., then performs route search from the present position or the start point to the destination or the crossing point, and performs guidance along the searched route. The route guidance system displays guide intersections such as an intersections etc. at which the vehicle should turn, then identifies and displays a road at which the vehicle exits out of the guide intersection. When performing route guidance at a distance to a peculiar object or a guide intersection in the middle of journey by displaying a map and etc., and the system often displays peculiar information regarding the guide intersection by switching from the map of the guide intersection to an enlarged intersection image when approaching the guide intersection. Thus, the guide intersection and the road exiting out of the intersection can be displayed easily by enlarging the intersection image thereof.
However, some of the previously proposed systems have an enlarged scale set at uniform rate prior to drawing the vicinity of the intersection as an enlarged intersection map by enlarging from a normal guide map on the basis of map data read out of the memory and, therefore, quite frequently cause an inconvenience. For example, if it is determined that an enlarged scale rate for drawing the intersection is increased in order to increase visibility as much as possible at a normal intersection, when drawing a large rotary as the enlarged intersection image, a road entering into the intersection and a road exiting out of the intersection results in being placed off the screen which disables those routes to be identified. On the contrary, when drawing all intersections including a large rotary etc. in order to accommodate them within a drawing limit, the enlarged scale rate has to be quite smaller. However, if the enlarged scale rate is to be a little too small on the basis of an intersection such as a large rotary, when drawing an enlarged intersection image, of a normal intersection such as a crossroads and a junction of three roads, unnecessary surrounding roads are also displayed due to the fact that the drawing limit area becomes wider. As a result, the unnecessary road impairs visibility of the desired intersection.
The invention provides a way to increase visibility of the guide intersection by drawing not only a normal intersection, but also a large rotary and etc. on the basis of an appropriate enlarged scale rate for each situation.
In order to attain this visibility, a navigation device is described that performs guidance along a route by making an intersection image by controlling a drawing area surrounding the intersection on the basis of information and a route regarding the intersection existing on said route which requires guidance.
Further, the invention comprises a map information memory for storing map information including information of a road and an intersection, a route search unit for calculating a route based on map information of map information memory, a route memory for storing route information calculated by the route search unit, a display control unit for making an intersection image regarding an intersection requiring guidance on the basis of the map information stored in the map information memory means and the route information stored in the route memory. The display control unit makes the intersection image upon determining an area of drawing the intersection image on the basis of information of the intersection which requires the route information and the guidance. Further, the display control unit judges whether the intersection which requires the guidance is larger than a predetermined image limit, if the intersection which requires guidance is larger than the predetermined image limit, the display control unit controls a display area with a reduction of the scale rate so as to display the entire intersection. Otherwise, the display control unit controls the display area so as to display all of the routes within the intersection.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.